An aircraft engine comprises a nacelle in which the engine itself is housed. The nacelle, which takes an annular form, has, at the front, an air input structure.
By convention, the terms “front” and “rear” are used throughout the text by taking the front and the rear of the engine as reference.
The air input structure globally comprises an internal face and an external face in contact with the outside air, while the internal face delimits a jet which constitutes the fan case ducting.
The function of the air input structure is, in particular, to ensure the aerodynamic flow of the air, on the one hand, to the fan case ducting, and, on the other hand, to the outside of the nacelle.
The air input structure comprises an air input lip, a front reinforcement frame, an acoustic panel and an external panel.
The air input lip has a U-shaped section open to the rear. It forms the outer jacket of the front part of the air input structure and it ensures the distribution of the air between the part which penetrates into the fan case ducting and the part which flows around the nacelle.
The external panel extends the air input lip on the external side and constitutes a part of the external face.
The front reinforcement frame also has a U-shaped section open to the rear and it is placed inside and to the rear of the air input lip. The front reinforcement frame ensures the mechanical strength of the front part of the nacelle and assists in preserving the shape and the dimensioning thereof.
The acoustic panel forms the internal jacket of the nacelle, behind the air input lip, on the side of the fan case ducting. The acoustic panel therefore constitutes a part of the internal face. The acoustic panel has a structure designed to attenuate the noises and is of composite sandwich type.
It may be that the air input lip is subjected to impacts that can damage it.
Repairing the air input lip then consists in cutting the part of the air input lip which is around the damaged zone, in conforming a plate for it to take the form of the cut part, then in fixing the plate using splices.
The splices are placed inside the air input lip straddling the conformed plate and the skin of the air input lip remaining in place. Each splice is then fixed by screwing or riveting from the outside.
To ensure that the screw or rivet heads are flush with the outer surface of the skin of the air input lip, it is necessary to produce a countersinking in the skin of the air input lip from the outside. The depth of the countersinking is conventionally of the order of 1.3 mm and the thickness of the skin of the air input lip must therefore be greater and is conventionally between 1.6 mm and 2 mm.
Although such a repair procedure gives satisfactory results, it is necessary to provide a relatively great skin thickness all along the leading edge of the air input lip, which is detrimental from the point of view of weight and therefore of fuel consumption.